The escalating requirements for high density and performance associated with ultra large scale integration require responsive changes in conductive patterns, which is considered one of the most demanding aspects of ultra large scale integration technology. High density demands for ultra large scale integration semiconductor wiring require increasingly denser arrays with minimal spacing between conductive lines. This objective becomes particularly difficult to achieve given the economic pressure for high speed production. Thus, the combined requirements of high speed and high density conductive wiring patterns pose a challenge which, to date, has not been satisfactorily achieved.
A traditional method for forming a dense array of conductive lines comprises the use of a subtractive etch back step as the primary metal-patterning technique. This traditional technique basically comprises forming a dielectric layer on a substrate, such as monocrystalline silicon, depositing a metal layer, such as aluminum, tungsten, polysilicon, tungsten silicide, or titanium silicide, forming a photo-resist mask having a pattern defining a dense array of conductive lines bordered by an open field wherein the distance between the conductive lines is considerably greater than the distance between conductive lines in the dense array, and etching through the mask. Typically, etching is conducted to optimize production speed as by utilizing an etching apparatus which generates a high density plasma, e.g., a high density chlorine plasma, which involves feeding chlorine gas, along with boron trichloride, into an etching apparatus, such as a Transformer Coupled Plasma (TCP) source type of apparatus. Model 9600, commercially available from Lam Research Corp., Fremont, Calif., has been found suitable. A high density plasma is generated with Cl.sup.31 as the etching species. Etching is conducted until the metal is substantially removed between the conductive lines of the dense array along with any residues which may have formed, and the underlying oxide etched to ensure complete removal of conductive material between the conductive lines. Other types of etching apparatus, such as other high density plasma source types of apparatus, can be used. For example, etching can also be conducted with an Electron Cycletron Resonance (ECR) type apparatus or a Helicon Resonant Inductive coupled plasma source type apparatus.
As employed throughout this application, the expression "open field" denotes an area wherein conductive lines are separated by a distance of at least 2.0 microns, while the expression "dense array" denotes a pattern of conductive lines which are separated by a distance of less than 1.0 micron.
In co-pending application Ser. No. 08/368,170, filed Jan. 3, 1995, a method is disclosed for solving the undercutting problem of conductive lines in a dense array bordered by an open field by reducing the initial etching severity. The disclosed invention comprises changing one or more of the original etching conditions at a strategic point during etching. The etching process is monitored in a conventional manner, as by optical spectrum monitoring, until the conductive material is substantially removed from the open field between conductive lines, but conductive material remains between the conductive lines of the dense array. It is at this point that undercutting of the conductive lines in the dense array commences and, it is at this strategic point that the initial etching severity is reduced by changing one or more of the initial etching conditions.
Co-pending application Ser. No. 08/423,495, entitled SEMICONDUCTOR DEVICE AND METHOD OF MANUFACTURING USING HIGH DENSITY PLASMA ETCHING (Docket No. 1033-098), addresses the undercutting problem which occurs in conductive lines of a dense array bordered by an open field in a manner which does not require manipulation of the etching process parameters or modification of the etching apparatus. In co-pending application Ser. No. 08/423,495 (Docket No. 1033-098), a semiconductor device and method of manufacturing the semiconductor device is disclosed, wherein undercutting of conductive lines in a dense array bordered by an open field is avoided by providing one or more, preferably one, non-functional or dummy conductive lines in the open field, wherein the distance between all the conductive lines is, preferably, essentially the same, typically below 1.0 micron, most preferably below 0.7 microns. The use of one or more non-functional or dummy conductive lines advantageously reduces undercutting in a bordering dense array of conductive lines without requiring the manipulation of any process variable and is, hence, cost efficient.
Upon further investigation and experimentation, I found that upon high density plasma etching a conductive layer to form a dense array of conductive lines, the etching species exhibits a differential trajectory path within the dense array of conductive lines. This differential trajectory path results in undercutting of the dense array of conductive lines on a dielectric layer containing functional components, such as lower conductive lines, bordered by an open field. Thus, there exists a need to develop techniques which further minimizes undercutting of conductive lines in a dense array.